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Cucurbit downy mildew confirmed in the northeast region of PA!

Posted: July 7, 2011

Downy mildew was confirmed on cucumber in a commercial field in Wyoming Co.
Upper and lower leaf symtpoms of downy mildew on cantaloupe. Purple sporulation is more sparse than on cucumber but it can be seen under a dissecting microscope. (Photo: Beth K. Gugino)

Upper and lower leaf symtpoms of downy mildew on cantaloupe. Purple sporulation is more sparse than on cucumber but it can be seen under a dissecting microscope. (Photo: Beth K. Gugino)

 

 

Late last week, downy mildew was confirmed on cucumber in a commercial field in northeast region of PA. The grower has since destroyed the hotspot in the field. It was also confirmed on cucumber in a 10 A field on the southern-most tip of Ontario, Canada across from Erie Co. as well as in Maryland, Delaware and now Ohio as of 7 July. There is moderate risk of spread to cucurbits in eastern half of PA from sources along the east coast and in the northwest region of PA from sources in Canada and Ohio.

 

 

There have also been several reports from growers in the same region about problems with muskmelon that are currently in the process of being identified and we are unsure whether or not it is downy mildew.

There currently are five recognized pathotypes (pathotypes differ in their ability to infect different types of cucurbits) of downy mildew. Cucumber and cantaloupes are susceptible to all five, while winter squash and pumpkin are only susceptible to pathotype 5 (see table below).

Pathotype 1
2
3
4
5
Host




Cucumber (Cucumis sativus)
+
+ +
+
+
Netted melons (C. melo var. reticulatus)
+ + +
+
+
Pickling melons (C. melo var. conomon)

+
+
+
+
Bitter melons (C. melo var. acidulous)

  +
+
+
Watermelon (Citrullus lanatus)

 
+
+
Winter squash and pumpkin (Cucurbita spp.)

 

+

It is important to be scouting all your cucurbit fields frequently. When the conditions are favorable, this disease can move very quickly. At this point, consider incorporating a translaminar downy mildew specific product into your spray program for cucumbers and muskmelon.

 

Downy mildew fungicide management: Fungicides with broad spectrum protectant activity (e.g. chlorothalonil, mancozeb and copper) will provide some downy mildew control and are good to use before disease develops in a production area. Once downy mildew is observed in your field or in other fields in the area, be ready to quickly switch to a mobile/systemic fungicide. Under conducive conditions, downy mildew can move quickly through a field so mis-timing or delaying a mobile/systemic fungicide can have a significant effect on yield. Also the application of these products under significant disease pressure increases for resistance to develop and makes the disease outbreak more difficult to control. For resistance management, always tank mix downy mildew specific products with a protectant such as mancozeb or chlorothalonil. In university efficacy trials in the Northeast, Presidio has performed better than Ranman and Previcur Flex followed by Curzate and Gavel (already contains mancozeb) which are considered slightly better than Forum, Reason, Tanos and Revus.

 

Please visit the Cucurbit Downy Mildew Forecasting website (http://cdm.ipmpipe.org) for the latest list of disease outbreak locations and forecasts. This information is updated by the end of the day on Monday, Wednesday and Fridays. Please let me know if you suspect downy mildew. Your reports help improve our ability to accurately forecast the movement of the pathogen and disease development.